Bordetella bacteriophages generate diversity in a gene that specifies host tropism for the host bacterium. This adaptation is produced by a genetic element that combines transcription, reverse transcription and integration with site-directed, adenine-specific mutagenesis. Necessary to this process is a reverse transcriptase-mediated exchange of information between two regions, one serving as a donor template region (TR) and the other as a recipient of variable sequence information, the variable region (VR).
Bordetella species that cause respiratory infections in mammals, including humans, serve as hosts for a family of bacteriophages that encode a unique diversity-generating system which allows the bacteriophage to use different receptor molecules on the bacteria for attachment and subsequent infection (Liu, M. et al. Reverse transcriptase-mediated tropism switching in Bordetella bacteriophage. Science 295, 2091-2094 (2002) and Liu, M. et al. Genomic and genetic analysis of Bordetella bacteriophages encoding reverse transcriptase-mediated tropism-switching cassettes. J. Bacteriol. 186, 1503-17 (2004)). The Bordetella cell surface is highly variable as a result of a complex program of gene expression mediated by the BvgAS phosphorelay, which regulates the organism's infectious cycle (Ackerley, B. J., Cotter P. A., & Miller, J. F. Ectopic expression of the flagellar regulon alters development of the Bordetella-host interaction. Cell 80, 611-620 (1995); Uhl, M. A. & Miller, J. F. Integration of multiple domains in a two-component sensor protein: the Bordetella pertussis BvgAS phosphorelay. EMBO J 15, 1028-1036 (1996); Cotter, P. A. & Miller, J. F. Bordetella. In Principles of Bacterial Pathogenesis. E. Groisman, Ed. Academic Press, San Diego, Calif. pp. 619-674 (2000); and Mattoo, S., Foreman-Wykert, A. K., Cotter, P. A., Miller, J. F. Mechanisms of Bordetella pathogenesis. Front Biosci 6, E168-E186 (2001)).
Bacteriophage (“phage”) BPP-1 preferentially infects virulent, Bvg+ Bordetella bacteria due to differential expression of phage receptor, pertactin (Prn), on the bacterial outer membrane (see FIG. 1a herein and Emsley, P., Charles, I. G., Fairweather, N. F., Isaacs, N. W. Structure of the Bordetella pertussis virulence factor P.69 pertactin. Nature 381, 90-92 (1996); van den Berg, B. M., Beekhuizen, H., Willems, R. J., Mooi, F. R., van Furth, R. Role of Bordetella pertussis virulence factors in adherence to epithelial cell lines derived from the human respiratory tract. Infect Immun 67, 1056-1062 (1999); and King, A. J. et al. Role of the polymorphic region 1 of the Bordetella pertussis protein pertactin in immunity. Microbiology 147, 2885-2895 (2001)). At characteristic frequencies, BPP-1 gives rise to tropic variants (BMP and BIP) that recognize distinct surface receptors and preferentially infect avirulent, Bvg− bacteria or are indiscriminate to the Bvg status, respectively. These viral parasites have thus evolved to keep pace with the dynamic surface structure displayed by their target host as it traverses its infectious cycle.
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